Thermoluminescent dosimetry, commonly referred to as TLD, is a technique for radiation dose measurement. A thermoluminescent (TL) material after having been exposed to an incident flux of charged particles such as beta rays, uncharged particles such as neutrons, or electromagnetic energy such as gamma rays and x-rays, will emit light when heated. When the emitted light is measured as a function of the temperature of the TL material over time, a glow curve is produced. The glow curve can be analyzed to determine the quantity of radiation to which the TL material had been exposed.
TLD systems have been developed for monitoring the exposure of personnel who work in the vicinity of radioactive materials, x-ray equipment, etc. Each person being monitored is issued a badge to wear so that the badge will be exposed to the same type and dosage of radiation as is the person wearing the badge. Although different types of badges have been used, one commonly used badge consists of an outer holder that houses a TLD card insert usually containing two, three or four TL elements. The TL elements are sandwiched between two sheets of transparent Teflon polytetrafluoroethylene (PTFE) that encapsulate the TL elements, and this sandwich is secured between two aluminum plates that have aligned holes forming respective windows for the TL elements.
Periodically the TLD cards are processed through a TLD reader to produce an exposure record for each person being monitored. In the TLD card reader, the TL elements in each card are heated and the thermoluminescence as function of TL element temperature is measured as by using a photomultiplier tube. The photomultiplier tube response is processed electronically to provide a measurement of TL integrals and/or the glow curve. After the cards have been read, the TL elements typically are annealed so that they can be used again.
Various methodologies have been devised for maintaining a chain of custody of the TLD cards and badges so that the reported dose for each TLD card may be reliably related back to the person who had worn that card. To facilitate the distribution, collection and reading of the TLD cards and the correlation of the TL data to the individuals wearing the badges, the TLD cards, and the holders as well, have been provided with machine readable bar codes. The machine readable bar codes enable automatic card and/or holder identification by a TLD card reader and also direct input of the identification codes into a computer monitoring system, thereby avoiding manual keyboard entry and the potential for human error associated therewith. When a card and holder are issued to an individual, the identification numbers of the card and holder assigned to the individual are stored with the individual's name in a database along with other desired pertinent data such as card type, date of last anneal, date issued, current location of the card and holder, etc. The cards and holders may be issued at a main distribution center to which the cards and holders are returned for processing through the TLD reader or at one or more remote site issue stations. The name of the person to whom each card and holder have been issued may be included on a label applied to the holder for easy identification, as may other information as well.
While chain of custody systems have been developed and used for whole person radiation monitoring, an effective and reliable chain of custody system heretofore has not been developed for extremity monitoring which is primarily concerned with the exposure of different parts of the body, rather than the whole body, to non-ionizing or non-penetrating radiation such as charged particles, beta particles and exotic particles. The above mentioned TLD cards and holders are unsuitable for extremity monitoring because of their large size and bulkiness. Extremity dosimeters are typically small and have been carried in various wearing devices such as rings, bandaid-type devices, finger sacks and gloves. A commonly used extremity dosimeter has TL material mounted to a disc that can be inserted into a ring for wearing. Recently, a number has been printed on the discs to permit identification of the disc independently of the ring which holds the dosimeter. Although thus numbered, a TLD system has not been devised which has provision for machine reading of the identification number printed on the discs and hence manual entry of the identification number necessarily has been involved.
Another but unsuccessful approach to extremity dosimetry involved the use of a finger ring dosimeter in the form of a thin strip or band. The dosimeter band had at one end thereof a quanity of TL powder material sandwiched between two sheets of material that were bonded to one another in some manner. Also sandwiched between the two sheets was a label bearing a machine readable bar code and a corresponding human readable identification number. To read the dosimeter, the two sheets would be pulled apart to free the TL powder for reading. One consequence of this is that the prior integral relationship between the active TL material and the identification bar code would be lost and consequently there would be a break in the chain of custody, such that the now loose identification bar code could inadvertently become associated with the wrong TL material. Another drawback is that the dosimeter could not be used more than once.